This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Data sets we have obtained from previous studies suggest a large (>200 msec) difference in BOLD onset timing due to differences in stimulus strength: stronger responses may begin earlier than weaker ones. Although stimulus strength (such as contrast amplitude) is thought to result in small onset timing differences in the neural response in the LGN (Hartveit and Heggelund 1992), V1 (Reich et al 2001), and other visual areas (Gawne et al 1996), these small timing differences (10's of msec) are an order of magnitude smaller than what we have seen in the BOLD fMRI response. We propose to make fine measurements of the timing of the BOLD response using an fMRI sequence with a short TR, gathering one volume every 250 milliseconds. Should timing differences as a function of response strength exist, they would have a substantial impact in the field, as an increasing number of studies are investigating timing of neural response using fMRI. The timing differences may also impact work using dynamic causal modeling (DCM), in which timing is used to infer causal links between cortical areas (Stephan et al 2008, Mechelli et al 2003). The data obtained here will be key for several grant proposals which propose to use fMRI and joint fMRI/EEG to study timing of perceptual processes. Engel, Olman, Kersten, and He all have interests or proposals under development in which such measurements of timing may play an important role.